True Bearing Research Articles

Some observations on the Orfordness rotating beacon

The following paper gives an account of observations which have been made during the past nine months on the Orfordness beacon which was established in July 1929 with the object of ascertaining the utility of this type of wireless aid to navigation when the observations were made by the personnel of the Mercantile Marine.The Orfordness beacon is of the rotating-loop type which operates on a wave-frequency of 288.5 kilocycles per sec. (wavelength 1040 m), and emits continuous navigation signals with special morse characters to indicate the N. and E. signal positions. Bearings are obtainable with any type of wireless receiver with the aid of a suitable stop-watch or chronograph. At the request of the Board of Trade, the masters and operators of many ships have submitted a record of the observations of bearings which they have made on the beacon, together with information as to the position and true bearing of the ship at the time the observations were made. The paper gives a summary of the results contained in the reports submitted by about 160 ships and discusses these results in some detail. It would appear from the results analysed that with a normal type of one- or twovalve receiver, as employed in modern ships, the reliable working range of the beacon is of the order of 100 miles by day or night. Within this range under favourable conditions about 80 per cent of the observed bearings are correct to within 2°. At greater ranges bearings of a slightly lower order of accuracy are obtainable in the daytime up to distances of about 250 miles with the same type of receiver, and with more sensitive receivers the working range may be anything up to 500 miles. At these larger distances, however, the reliability of the bearings is somewhat impaired during the hours of darkness by the phenomena of flat minima and wandering zeros which are characteristic of experience in direction-finding under similar conditions.Section (3) of the paper gives details of a series of observations which have been carried out at the National Physical Laboratory. From these it appears that the accuracy of the time of rotation of the beacon is well beyond the limit of any ordinary chronograph or stop-watch which is employed in bearing observations. From systematic readings obtained in the daytime over a considerable period, it is also to be concluded that skilled observers can obtain bearings from the beacon with a maximum error of 2°, and that a high proportion of the bearings are accurate to within 1°. These results, together with those (already referred to) taken on board ship, indicate that no definite error can be ascribed to the rotating beacon installation itself. Over the range of 93 miles overland between Orfordness and Teddington, observations taken at night show that the accuracy of bearings, even with skilled observers, seriously deteriorates and errors of as much as 20° may sometimes be experienced. Since it appears that the working range of the beacon might with advantage be increased above its normal value of Reprinted from 100 miles oversea, it will be desirable in future to develop the beacon along lines which will provide freedom from these night errors, which at present appear to be the only limitation imposed upon the accuracy and reliability of the bearings supplied by the rotating-loop type of transmitter.

A Chart Showing the True Bearing of Rugby from All Parts of the World

A Chart Showing the True Bearing of Rugby from All Parts of the World

Contact effects between electrodes and dielectrics

This report covers a research on the phenomena of so-called “contact resistance”. The research was carried out, on the suggestion of the E.R.A., by the Metropolitan-Vickers Electrical Co., Ltd., and the results show the nature and importance of contact phenomena, also their true bearing on resistivity and dielectric-loss measurements, and that certain conclusions reached by a previous investigator were exaggerated.The authors give a detailed account of a series of experimental investigations and describe the development of methods for the determination of the actual resistance and capacitance of the interface between electrodes and dielectrics.Section (I) of the report deals with two methods which demonstrate the existence of a potential drop across the contact face but which do not lend themselves to accurate quantitative work. A third method is described in which the potential distribution along a cylindrical specimen, subjected to a known d.c. voltage, is ascertained by means of exploring electrodes, and the contact voltage-drops deduced. From these, and the known resistance of the specimen, the contact resistances at each electrode are obtained in ohms per cm2. In the case of slate this was found to be 0.8 to 0.9 × 106, and fibre 5 to 9 × 106.Since the contact voltage-drop with direct current is not affected by direct-contact capacitance effect, a fourth method was developed in which the current and watt-loss were measured for a given a.c. stress of known frequency. From these measurements the equivalent series resistance and capacitance of the specimen can be calculated. The specimen was then machined down to a different thickness and similar calculations were made for a range of thicknesses. These factors plotted against thickness and extrapolated to zero thickness revealed the residual quantities attributable to the interface. In Table 6 it is shown that, over a wide range of power factors, the contact resistance does not vary greatly, it being of the same order as already determined.Ultimately the potential distribution method, previously adopted for direct current was modified for a.c. determinations and a large number of tests were carried out on slate, fibre and bakelite. Table 9 gives a complete summary of the results of 75 tests, including a number of check tests to ascertain the effect of frequency, voltage stress, humidity, temperature, surface leakage, roughness of surface and dirty mercury. Tests 53 to 69 were carried out with electrodes other than mercury. The results are important in that they reveal methods of obtaining better contact than can be obtained by the use of a simple mercury electrode.For comparative purposes the authors give in Table 11 the maximum, minimum and mean values of contact resistance and capacitance for normal conditions at 50 cycles and show that the agreement obtained between the two a.c. methods mentioned above is as good as the agreement obtained in different tests by any one method.The significance of the contact effect in relation to measurements on dielectrics is discussed, certain typical conditions being postulated and the percentage error in power factor and permittivity shown to be negligible except in the case of thin specimens of low-grade material. In the extreme case of a hypothetical material 1 mm thick, having a power factor of 80 per cent, the error attributable to contact impedance is shown to be 18 per cent, while in a more normal case where the power factor is 5 per cent and the thickness 1 cm, the error is appreciably less than 1 per cent.

VIII.—Instances of Orientation in Prehistoric Monuments of the British Isles

The occurrence of orientation in prehistoric structures has long been noticed. It has not, however, received from investigators much more than a passing comment, such as ‘the barrow is directed to the eastward’, or ‘the entrance to the chamber faces the north-west’. If a definite bearing is given, it is rarely stated whether it is ‘Magnetic’ (such as is obtained from a prismatic compass), or a True Bearing, i. e. an azimuth.

The Direction and Intensity of Waves from European Stations

The deviations of radio goniometric readings from the true bearing of distant and nearby stations were measured at a suitable location with a coil antenna and receiver. In addition to errors due to physical obstructions in the path of the incoming wave, errors varying with the time of day were measured. Radio goniometric measurements were also made during an intense aurera. The intensity of the field of the incoming signals was also measured by means of a resistance network, and the necessary apparatus is described.

Battles, Ancient and Modern

In the last number of the Hellenic Journal Professor Burrows has once more attacked Pylos and Sphakteria, this time with the aid of certain allies from the Peloponnese and a whole battery of photographs. I am, I confess, loth to dye this ink-stained field a deeper hue, and I have certainly no intention of sending friends of mine to Pylos with a view to reviving a controversy which has gone far enough. At the same time I do not wish to appear to undervalue the evidence of Messrs. Carr Bosanquet, Crowfoot, and Lindsay, though it is not of a very decisive character. I should therefore like to point out, as briefly as possible, its true bearing, and in doing so I have the satisfaction of not having to treat it as hostile, though brought into court by the other side.

The Evidences of the Geological Age and Human Manufacture of the Fossil Flint Implements

Amiens and Abbeville do not, however, enjoy a monopoly in these flint implements; they are found, apparently, all over the earth. At any rate, we can boast in our land of such treasures, and we can proudly record that the first discovered specimens belong to England. Let Amiens and Abbeville by all means be commemorated as the scenes of M. Boucher de Perthes' persevering investigations, which have furnished the incitement to the present remarkable inquiry—let the names of Boucher de Perthes, Prestwich, Falconer, Flower, and Evans, be duly honoured as the pioneers of the investigation; but let us also think of Hoxne, Grays, Ilford, Maidstone, Stanway, and the scores of other places where mammalian bones have been found in our own land—and, let us hope that our young geologists will set to work, and reap a rich harvest in the yet ungarnered fields. Does not this first recorded implement—this earliest discovered relic—(fig. 5) treasured and preserved in the Sloane collection, the nucleus of the British Museum, and entered in that old catalogue, two hundred years ago—encourage them. Does it not say in unmistakable language “Under your feet these relies may be found?”There is another of these spear-shaped flints, which has obtained a great deal of notoriety in the late discussions. It was found at Hoxne, in Suffolk—a place memorable in the history of the good king Edmund, the saint and martyr—and was described, and figured in the “Archæologia,” (see cut 9, p. 20), by Mr. Frere, the finder, who, with remarkable acuteness, seems to have fully comprehended the value and true bearing of his discovery. His paper is, even now, an excellent epitome of the subject; and we give it at length, just as it was read in 1797, before the Society of Antiquaries of London.

On the Geology of Strath, Skye

The first notice of the district described in the present paper was that published in 1800 by the late Professor Jameson in his ‘Mineralogy of the Scottish Isles.’ It is exceedingly meagre, having been compiled from the notes of a brief excursion in bad weather, and contains only a list of minerals found in the ascent of Beinn na Cailleaich, with the mention of numerous basalt-veins that traverse the limestone in every direction. Eighteen years later Dr. Macculloch published his ‘Description of the Western Islands’ wherein he pointed out the existence in Skye of secondary strata—the equivalents of the lias and oolite of England, extending in broken and irregular series up to what has since been determined to be the equivalent of the Oxford Clay. He also described with considerable minuteness some of the more remarkable features in the geology of Strath. Yet of the structure of the district he seems to have had but a vague general idea—not a few of its most important features having escaped his notice, while of some of the facts which he mentions he has failed to perceive the true bearing. I shall even have occasion to show that, notwithstanding the minuteness of his description, he can only have examined a limited portion of the district, and that too but superficially. Several years later Sir ttoderick Murchison examined the eastern coast-line of Skye, and, from a comparison of fossils, ascertained the existence and limits of strata belonging to the lias, and the lower and

On the Geology of Strath, Skye

This paper will be published in the next line Number of the Journal.